This invention relates to a laser apparatus including electric power supply system for supplying electric power to a laser oscillator and a cooling water supply system for supplying cooling water to the laser oscillator.
An example of such a laser apparatus is a laser beam machining apparatus. The laser beam machining apparatus employs a high power supply to obtain a high laser output from the laser oscillator. To increase the laser oscillation efficiency and stabilize the laser performance, the laser beam machining apparatus includes a cooling water supply including a storage tank and a pump for forcedly cooling the laser oscillator with cooling water.
The electric power and cooling water supply systems are externally supplied with a required electric power, signals and primary cooling water and required outputs signals and drainage water. A solid state laser apparatus such as a YAG laser uses pure cooling water having a high electric insulation since the cooling water passes through an electrode of the pumping lamp within the laser oscillator. To maintain the purity of the cooling water, an ion exchanger and a filter are included in the cooling water supply system. Such an ion exchanger and filter are consumable parts and must be regularly replaced.
FIG. 12 shows an overall arrangement of a prior art appratus for cooling a solid state laser oscillator. In the cooling apparatus, cooling water is pressurized by a pump 202 and circulates through a storage tank 200, filter 204, laser oscillator 206, heat exchanger 208 and ion exchanger 210 by way of pipes. Within the laser oscillator 206, the cooling water passes through glass tubes respectively containing a laser rod and a pumping lamp, and through a water passage disposed in the oscillator block.
The water flowing out of the laser oscillator 206 is cooled by the heat exchanger 208 and returns to the storage tank 200. Most of the cooling water drawn by the pump 202 from the tank 200 is supplied to the laser oscillator 206 through the filter 204 whereas the remaining fraction of the water passes through the ion exchanger 210 which deionizes the cooling water so that purified water is fed back to the tank 200. The ion exchanger 210 is of a cartridge type only allowing a limited flow of water to pass therethrough. Due to the flow limitation, the ion exchanger 210 is connected in shunt with the laser oscillator 206, so that the ion exchanger 210 receives only a fraction of the cooling water drawn by the pump.
Flow control valves 212 and 214 are connected in series and in parallel, respectively, with the ion exchanger 210. A thermosensor 216, pressure sensor 218 and electric conductivity sensor 220 are connected in the pipeline between the pump 202 and the laser oscillator 206 to monitor the temperature, pressure and electric conductance, respectively, of the cooling water supplied to the laser oscillator 206. Reference numeral 222 denotes an electric motor for driving the pump, 224 denotes a flow switch, 226 denotes a tank drain, and 228 denotes an electromagnetic valve.
In the prior art laser apparatus of this kind, a visual display and a keyboard are disposed on the front panel of the apparatus whereas those parts for which maintenance, repair, connecting and exchange are required, such as the external electric connecting terminal circuit breaker of the power supply, external pipeline connecting port, tank, ion exchanger and filter, of the cooling water supply are disposed on the back of the apparatus.
Thus, maintenance personnel must gain access to the back of the apparatus when repair, wiring and/or parts exchange is required. The apparatus of this kind is normally installed with its back against a building wall. To do the maintenance work, the apparatus must be moved to a place spaced well away from the building wall.
Although it is about the size of household refrigerator, the laser beam machining apparatus is much heavier than the household refrigerator. A typical YAG laser apparatus (including laser oscillator, power supply and cooling system) weighs about 250 to 350 kilograms. For portability, the laser apparatus has casters on the bottom thereof. Frequent movement of such apparatus not only requires a sufficient space around the apparatus but also can cause errors and failures due to vibration in the optical system of the laser oscillator.
The prior art laser oscillator cooling apparatus is large because of the considerable space occupied the filter 204 and the ion exchanger 210 for maintaining purity of the cooling water in addition to indispensable components including the storage tank 200, pump 202, motor 222 and heat exchanger 208. The provision of the filter 204 and the ion exchanger 210 complicates the pipes, joints and fittings, increasing the cost and causing leakage of water because of the increased number of connecting points.
The flow limitation of the cartridge type ion exchanger 210 requires that only a fraction of the cooling water drawn by the pump 202 passes to the ion exchanger 210 that an ion exchanging process is performed bit by bit. Thus, the ion exchanging efficiency is reduced. Although a plurality of ion exchangers may be provided in parallel to increase the ion exchanging efficiency, this involves increasing the number of pipes and joints as well as the ion exchangers, thus entailing further serious problems of increased cost and leakage of water.
The performance of solid state laser oscillators is seriously influenced by the cooling effect. A slight temperature change in the supplied cooling water can result in a large change in the laser output. In this regard, a thermal control means is provided in the tank 200 to maintain the temperature of the cooling water.
The temperature keeping control is not enough to provide a stable operation of the laser oscillator. It is necessary to add a flow control means which controls the flow of the cooling water. A constant cooling effect is obtained by maintaining both the temperature and the flow of the cooling water.
In the prior art cooling apparatus, however, a revolution speed change of pump 202 due to changeover between different electric commercial power frequencies (50 Hz, 60 Hz) has caused a change in the flow rate, resulting in an unsatisfactory operation of the laser oscillator 206. To overcome the problem, an adjustable flow control valve is used for the valve 214 to adjust the flow rate in correspondence with the available commercial power frequency. However, the adjusting work is complicated and troublesome.